The present invention relates to an irradiation device for irradiating plants, comprising a carrier element defining a culture plane E for cultivating the plants, multiple irradiation sources for irradiating the plants with visible and/or ultraviolet radiation, and multiple infrared emitters for irradiating the plants with infrared radiation.
The present invention further relates to an emitter module for irradiating plants with infrared radiation for use in an irradiation device.
For the breeding and cultivation of plants, for example in greenhouses and in tiered crop growing, artificial light sources are used. The emission spectrum of these light sources is usually adapted to the absorption spectrum of the green leaf pigment of chlorophyll and carotenes
Several natural pigments that are essential to the photosynthesis process are combined under the terms chlorophyll and carotene. The absorption spectra of these pigments dissolved in solvents have two pronounced absorption maximums, namely one absorption maximum in the violet and blue spectral range between 400 nm and 500 nm, and another absorption maximum in the red spectral range of visible light between 600 nm and 700 nm.
To ensure efficient irradiation of plants, the emission spectrum of artificial light sources for irradiating plants has large radiation components in both wavelength ranges specified above.
As light sources, for example, gas discharge lamps or light emitting diodes (LEDs) are used. Gas discharge lamps consist of a discharge chamber filled with a filling gas and in which two electrodes are arranged. A gas discharge associated with the emission of visible radiation takes place in the discharge chamber as a function of a voltage applied to the electrodes. The wavelength of the emitted radiation can be influenced by a selection of the filling gas and adapted to the absorption spectrum of the chlorophyll, for example by an appropriate doping of the filling gas. In contrast, LEDs emit light only in a limited spectral range, so that, for generating an emission spectrum adapted to the absorption spectrum of the chlorophyll, multiple LEDs of different wavelengths must be combined with each other. For example, from U.S. patent application publication 2009/0251057 A1, an artificial light source is known having multiple LEDs in which, for generating artificial sunlight, light emitting diodes having different emission spectra are combined.
However, efficient cultivation of plants depends not only on the excitation of photosynthesis, but also on the transport of water and nutrients in the plant and on the carbon dioxide assimilation. Both the water and nutrient transport in the plant and also the carbon dioxide assimilation are influenced by the stomatal apparatus of the plant. By the stomata of the plant, the plant regulates the gas exchange with the ambient air, in particular the absorption of carbon dioxide from the air and the emission of oxygen to the air. The water balance of the plant is also influenced by the opening width of the stomata. Thus, opened stomata lead to increased water evaporation that generates transpiration suction, so that, overall, the transport of water and nutrients (sap flow) from the roots to the leaves is increased.
The opening width of the stomata can be regulated by several factors that include, for example, the temperature, the availability of water, the carbon dioxide concentration in the leaf interior, and the absorption of light. By a targeted irradiation with infrared radiation, the stomata width and thus the effectiveness of photosynthesis can be regulated.
In International patent application publication WO 2010/044662 A1, an irradiation device for plants is proposed having a chamber in which, in addition to the radiation sources for irradiating the plants with visible or ultraviolet radiation, multiple infrared emitters arranged on a side wall of the chamber are provided for irradiating the plants with infrared radiation. By the infrared emitters, the leaves of the plants are heated such that the stomata open, so that a stimulation of the exchange processes of the plants with their surroundings is achieved.
Due to the lateral arrangement of the infrared emitters, the individual plants are irradiated as a function of the their planted position on the culture plane each at a different spacing to the infrared emitters and are therefore irradiated to different degrees. It has been shown that, in particular, compared with the inner areas of the culture area, the outer areas of the culture area are exposed to higher irradiation intensities. To ensure efficient cultivation of the plants, however, in principle uniform growth of the plants and thus homogeneous irradiation of all plants is desirable.
With a lateral arrangement of the infrared emitters in relation to the cultivation surface, a large number of emitters is required, which must have a low power output in order not to damage the plants in the outer area of the culture area due to excessive heating. Infrared emitters, however, typically have a high power output; emitters of low power output are complicated to make and have only a limited service life.
In addition, the lateral arrangement of the infrared emitters also contributes to irradiation and heating of the other components provided in the irradiation device, for example the electrical cables and mounting elements for the radiation sources, and also the radiation sources provided in the irradiation device, whereby the service lives of these components are shortened due to the irradiation. A lateral arrangement of the infrared emitters is therefore associated with high operating costs.